Engines may increase output power by using boosting devices that compress intake air. Since charge compression increases air temperature, charge air coolers may be utilized downstream of a compressor to cool the compressed air, further increasing the potential power output of the engine. As intake air passes through the charge air cooler and is cooled below a dew point, condensation occurs. The condensate may be accumulated at a trap and delivered to the engine subsequently, e.g., during steady-state or cruise conditions, at a controlled rate of ingestion. However, because the ingested water slows the rate of combustion, even small errors in the introduction of water into the engine can increase the likelihood of misfire events. Engine control systems may employ various misfire control approaches to reduce misfires caused by the ingestion of water.
One example approach for addressing moisture induced misfires is shown by Tonetti et al. in EP 1607606. Therein, an intake air flow rate is adjusted based on an oxygen concentration of recirculated exhaust gas to compensate for condensate in the EGR. Another example approach is shown by Wong et al. in U.S. Pat. No. 6,748,475. Therein, a fuel injection and spark timing is adjusted based on a parameter indicative of an oxygen concentration or water concentration of recirculated exhaust gas. This allows misfire events arising during steady-state conditions due to a sudden ingestion of too much water or condensate to be reduced. Even when the amount of water ingested is small, during a transient tip-in from steady state conditions, such as when going from low to moderate air mass flow rates to high air mass flow rates, the ingested water can cause slow combustion issues. In particular, the high air mass flow rate can break the surface tension of the condensate, and release from the charge air cooler where the engine ingests it in larger quantities.
However, the inventors herein have identified potential issues with such an approach. As one example, even with adjustments to intake air flow rate, fuel injection, and/or spark timing, misfires caused due to condensate ingestion during steady-state conditions may not be sufficiently addressed. Specifically, engine combustion stability during steady-state conditions may be sensitive to the amount of condensate. Consequently, even small errors in condensate metering can lead to misfires.
In one example, some of the above issues may be addressed by a method for a boosted engine comprising: downshifting a transmission gear to increase engine speed and increase engine airflow (air mass flow rate) in response to a deceleration event and a condensate level in a charge air cooler (CAC). The method may further include, increasing an opening of an intake throttle to increase airflow through the charge air cooler. In this way, condensate can be purged efficiently without incurring misfire events.
As one example, an engine controller may downshift a transmission gear to initiate delivery of condensate collected at a CAC to an engine during a deceleration event. For example, in response to a tip-out, when the engine is spinning un-fueled (e.g., during a deceleration fuel shut off or DFSO event), the vehicle may be downshifted from a transmission third gear to a transmission second gear to increase engine speed and manifold vacuum. Then, condensate may be pulled into the engine from the CAC. Additionally or optionally, an intake throttle may be opened to increase airflow to the engine and through the CAC. By opening the throttle during the deceleration, intake manifold vacuum generated from the spinning engine may be increased and used to increase purging efficiency.
In this way, by delivering condensate from a CAC to an engine during a deceleration event, the large amount of intake manifold vacuum generated from downshifting can be advantageously used to draw condensate into the engine. By delivering the condensate to the engine during conditions when cylinder combustion is not occurring, the condensate can pass through the engine system without degrading combustion stability. Further, since the condensate is introduced while no combustion is occurring, concurrent engine actuator adjustments for misfire control may not be required. Overall, a larger amount of condensate may be purged into the engine without increasing engine misfires.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.